Electrolytic cavity sinking apparatus



Sept, 27, 1966 L. A. WILLIAMS ELECTROLYTIC CAVITY SINKING APPARATUS 4 Sheets-Sheet l Filed sept.

of INVENTOR.

Sept. 27, 1966 L. A. WILLIAMS 32759543 ELECTROLYTIC CAVITY SINKING APPARATUS Filed Sept. 2, 1960 4 Sheets-Sheet 2 eff u INVENTOR;

Sept. 27, 1966 L A. wxLLlAMs ELECTROLYTC CAVITY SINKING APPARATUS 4 Sheets-Sheet 5 Filed sept.

INVENTOR.

Sept. 27, 1966 L.. A. WILLIAMS ELECTROLYTIC CAVITY SINKING APPARATUS United States Patent 3,275,543 ELECTROLYHC CAVITY SENKING APPARATUS Lynn A. Williams, Winnetka, Ill., assigner to Anocut iEngineertng Company, Chicago, lill., a corporation of lllinois Filed Sept. 2, 1960, Ser. No. 73,154 2 Claims. (Cl. 20d-224) This is a continuation-impart of copending application to Lynn A. Williams, Serial No. 772,960, filed November 10, 1958, now Patent No. 3,058,895, for Electrolytic Shaping.

The present invention relates to an electrolytic cavity sinking apparatus and method, and particularly to an apparatus and method for accurately forming a cavity in or through the work.

It `is contemplated that in the practice of this invention one may wish to utilize one or more inventions in the following copending applications:

Electrolytic Shaping, by Lynn A. Williams, Serial No. 772,960, tiled November 10, 1958, issued into Patent No. 3,058,895, dated October 16, 1962;

Electrolytic Shaping Apparatus and Method, by Lynn A. Williams, Serial No. 36,314, filed lune l5, 1960, now Patent No. 3,235,475;

Electrolytic Cavity Sinking Apparatus and Method, by Lynn A. Williams, Serial No. 35,647, tiled June 13, 1960, .now Patent No. 3,196,093;

Electrode for Electrolytic Shaping, by Lynn A. Williams, Serial No. 35,646, led June 13, 1960, now Patent No. 3,123,545;

Control and Operating System for Electrolytic Hole Sinking, by Lynn A. Williams and Iames E. Davis, Serial No. 863,246, filed December 3l, 1959, now abandoned;

Electrolyzing Electrode, by Lynn A. Williams, Serial No. 853,194, filed November 16, 1959, issued into Patent No. 3,120,482, dated February 4, 1964;

Electrode for Electrolytic Shaping, by Lynn A. Williams, Serial No. 849,595, filed October 29, 1959, issued into Patent No. 3,019,178, dated January 30, 1962;

Electrolytic Removal of Work Materials, by Lynn A. Williams, Serial No. 844,706, filed October 6, 1959;

Electrode for Electrolytic Hole Sinking, by Lynn A. Williams, Serial No. 800,276, filed March 18, 1959, now abandoned;

Electrolytic Hole Sinking, by Lynn A. Williams, Serial No. 814,450, led May 20, 1959, issued into Patent No. 3,002,907, `dated October 3, 1961;

Electrolytic Cavity Sinking Apparatus and Method, by Joseph L. Bender and Lynn A. Williams, Serial No. 37,766, filed June 21, 1960, now Patent No. 2,992,640.

lt is a principal object of the present invention to provide a `new and improved cavity sinking apparatus and method by means of which the size and dimensions of the cavity may be controlled within tolerances heretofore not thought possible.

Another object is to provide a new and improved electrolytic cavity sinking apparatus and method by means of which control may be had of the rate of feed of the electrode into the work, careful control of the voltage of the electrolyzing current can be exercised, and the ternperature and pressure of the electrolyte may be regulated so that the cavity maybe formed within the specified tolerances.

Another object is to provide a new and improved electrolytic cavity sinking apparatus and method, by means of which high production rates may be obtained while maintaining the desired tolerances above mentioned.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings, wherein race FIG. l is a schematic elevation of the complete apparatus;

FIG. 2 is a sectional View of the drivehead assembly for the apparatus shown in FIG. l;

FIGS. 3 and 4 are plan and elevational views of the dial indicator and depth limit control assembly which is included as part of the drivehead; and

FIG. 5 is a schematic circuit diagram.

Referring to FIG. 1, reference numerals 1, 1a, 1b, and 1c identify several parts of a weldment frame or base. Mounted on the base 1 is a drivehead 3 shown in more detail in FIGS. 2, 3, and 4. It constitutes generally an electromechanical drive arranged to move an electrode very smoothly, constantly, and precisely in its working relationship to a workpiece. lt includes an upper housing 5 (see also FIG. 2) and a lower housing 7. Projecting from the lower housing 7 is a ram 9 and a ramhead 11 to which is `fastened an insulating plate 13 and an electrode mounting plate 15. The ramhead and ram are sealed against electrolyte by a boot 17 (see FIG. 2). A pushrod 19 protected by a boot 21 links the ramhead 11 to a dial type depth indicator (FIG. l). Shown on the mounting plate is an electrode 22. in a holder 25 and a feed hose 27. Electric cables are also connected for operation, but are not shown.

The ram 9 is supported in ball bushings 29 for axial motion and is prevented from rotation by a cross pin carrying needle bearings running on hardened tracks (not shown).

Lead screw 31 and lead nut 33 coact to drive ram 9 forward and back. The lead screw is supported by suitably mounted thrust bearing 35 and radial bearing 37.

The lead screw is driven through -a sprocket 39 by a chain 41. An electric brake 43, spring biased to locking position, is mounted on the end of the lead screw 31. It is energized when running to release the brake, but deenergized when stopped, so as to arrest rotary motion of the lead screw and thus prevent overtravel beyond the desired limit.

The upper housing 5 contains the actual drive :mechanism. In FIG. 1 are shown a speed or feed rate adjustment knob and dial 45, a tachometer 47 Varranged to indicate the feed rate, a depth limit adjusting knob 49, a signal light 51 to indicate actuation ofthe spark detector system disclosed in copending application of Williams and Davis, Serial No. 863,246, led December 31, 1959, entitled Control and Oper-ating System. for Electrolytic Hole Sinking, and a signal light 53 to indicate actuation of the depth limit control system to be described later.

Within upper housing 5 (FIG. 2), the chain 41 is driven by a sprocket 55 which runs forward or back at higher or lower speed as driven by the following tmechanism. A reversible motor M drives through a variable speed transmission VST which is controlled by knob 45 (FIG. 1) acting through connecting linkage (not shown). A `further speed reduction is obtained through step down transmission 57. Controlled by selective actuation of electric clutches or 67, the output of transmission 57 is connected either at the same speed or `at a much higher speed to the sprocket 55.

If clutch 65 is engaged, power is transmitted through quill shaft 58 to shaft 59, and thence to sprocket 55. If the other clutch 67 is engaged, then a stepup in speed results as quill shaft 58 drives shaft 61 through gear and pinion 69 and 71 (about 4-1 ratio) and transmits power through the clutch 67 to a second gear and pinion 73 and (about 3-1 ratio) back to shaft 59 and thence to drive sprocket 55.

With this combination, actual motion of the ram can be controlled from very low speed of approximately .010l per minute up to .750 per tminute, all in the low speed range, and then, by electrical selection of the high speed range at about 12 times these speeds. The high speed range is used principally for positioning of the electrode with respect to the work.

Actual rate of feed is indicated on the ta-chometer 47 (FIG. 1) which is driven by conventional drive mechanism including (FIG. 2) gear and pinion 77 and 79 and flexible drive shaft 81. The tacholmeter is calibrated to read directly in inches per minute when the drive is in low speed configuration.

Reversal of direction is accomplished by electrical switching of circuit connections to the motor M in the well known manner. Console C (FIG. l) carries pushbuttons, as follows, to control the drivehead 3:

Forward, 83; Reverse S5; Normal Feed (slow speed), 37; Rapid Traverse (high speed), 89; Run, 91; Jog, 93; Emergency Stop, 95.

Addition-al buttons on the console are:

Pump On, 97; Pump Off, 99; Heater On, 101; Heater Off, 103.

Electrical cables 105 and 107 extend from the machine proper to the console C, which is movable to any convenient location 'adjacent the machine proper.

In operation, one actuates first either the forward or reverse button 83 or 85 and associated relay circuits. (Time delay relays are used to prevent full to full change of motor direction which might cause damage.) This starts the motor M in the desired direction, but neither the low speed clutch 65 nor the high speed clutch 67 is yet engaged. It is possible, however, to preset the feed rate by use of control knob 45 and by reference to tachometer 47. Then, one selects low (normal feed) or high speed (rapid traverse) by pushing the appropriate button. This preconditions the relay circuits for energizing one or the other of the electric clutches 65 or 67, but still does not energize either. This occurs only when one pushes the jog or run button 93 or 91, the former holding the circuit only while the button is manually depressed, the latter (run) maintaining the circuit through a holding relay. When either the jog or run button is pushed, electric brake 43 (FIG. 2) is released. Feed may be stopped by pushing the emergency stop button 95, which releases all circuits, or by pushing and releasing the jog button 93, which releases only the run circuit, leaving the set of forward or reverse and of normal feed or rapid traverse.

The buttons, where appropriate, may have integral pilot lights in them. The basic circuit diagram (FIG. 5) will he understood without further verbiage by those skilled in the art in light of the foregoing description of the mode of operation.

The rem-aining elements on console C relate to the power supply of direct current electrolyzing current. VM1-reads voltage at the power supply. VM2 reads voltage near the electrode and the work, the difference between the two showing the drop or loss through cables and connecting lugs, etc. AM reads the amperage passing between the electrode and the work through the electrolyte. Pilot lights PL1, PL2, and PL3 indicate, respectively, that the alternating current supply line is on; that the rectifier system is ready, its vacuum tube control elements being warmed up; and that the direct current power feed to the work gap is energized. Below PLI are ON and OFF but-tons 109 and 111 to control the standby condition of the rectifier control elements, and below PLS are ON and OFF buttons 113 and 115 to control energization of the power relay in the rectier system. Thus, power to the electrode and Work may be turned on or off without deenergizing the v-acuum tubes of the control system. Knob 117 controls the reference voltage to set the voltage delivered by the rectifier. It may be regarded as the equivalent of potentiometer R11 (FIG. 4), in copending application of George F. Keeleric and Eugene Mittelmann, Serial No. 381,278, iled September 12, 1953, for Electric Supply System for Electrolytic Grinding, now issued into Patent No. 3,117,919, dated January 14, 1964, to Eugene Mittelmann. Knob 119 is the bias or sensitivity control of the spark detector circuit of the type shown in copending application of Lynn A. Williams and James E. Davis, Serial No. 863,246, filed December 31, 1959, for Control and Operating System for Electrolytic Hole Sinking, and may operate a potentiometer corresponding `with R5 or R11 in FIG. 2 of that application. Signal light 53 corresponds with signal light of the same FIG. 2 of the same application.

Referring back to the above identified copending application of Keeleric and Mittelmann, it should be understood that the section of the circuitry marked Signal Amplifier as shown in FIG. 4 of that application, is not used, and it is to be considered with vacuum tubes identified as V-1b and V-la (in FIG. 4) as removed while the arm of potentiometer R-9 is moved to its lowermost position. At the same time, the circuitry for controlling the voltage may be improved by the inclusion of a voltage regulator tube in the circuit system which includes diode rectiiers D-2 and D-3 and condensers C-8 `and C-lti, so that the voltage which appears across the resistance of R-11 remains constant despite variations in line voltage or load. This is important, for in the present invention it is desired to maintain quite closely the potential between the electrode and the workpiece. This voltage, which normally falls between five volts and 18 volts, should be held for best results within about one to five percent of the nominal, preset voltage. T-o the extent, of course, that there is any inadequacy of the regulation of the power supply, this may be offset by manual `adjustment of the voltage control knob 117 (FIG. 1) by reference to voltmeter VM2. Here it should be noted that the pickup connections feeding the voltage balance and bias system of the above identified Keeleric `and Mittelmann application should be made, for best results, close to the electrolytic work gap between the electrode and the work. Thus, the control leads may be connected respectively to the xture holding the Work (not shown) and the electrode block or even the electrode itself. In this way the control system will compensate for any losses in voltage occurring because of IR losses in the cables and connections between the power supply unit and the work gap. (Here, see also the `above identified application of Williams and Daivis.)

Referring to FIG. 1, a grounding cable 121 is connected from the ram head 11 to the frame of the machine so that the ram head always remains at ground potential Ieven if there were to be la breakdown of the insulation of insulating plate 13 or some accidental contact between electrically energized parts of the electrode system and the ram head. By use of the grounding cable 121, I prevent or reduce passage of electric current through the bearings which support the ram head, which would be damaged if heavy current were to pass through them.

Still referring to FIG. 1, the entirety of the drivehead assembly is mounted on dovetail cross slides to permit horizontal motion of the entire drivehead assembly in the direction toward and away from the viewer looking at the drawing. This arrangement is conventional, and the motion is impar-ted by manual operation of hand wheel 123. A slide lock is also provided, and is controlled by handle 125. This locks the motion of the ram head so that once a desired setting has been obtained it will not be disturbed through accidental movement of hand wheel 123.

In order to hold the work, a stainless steel Worktable 127 is provided and is mounted upon ia vertical slide controlled by hand wheel 129. The entirety of the vertical slide assembly is protected against electrolyte by a collapsible rubber boot (not shown) which is sealed both to the worktable and to the bottom of a stainless steel pan which is at a level just above the upper limb of hand wheel 129. This pan has side walls which extend to Ei a height just below the bottom surface of worktable 127, as shown. The bottom of the pan has exit holes which drain back into electrolyte tank 130. An enclosure 131 for the work area is provided and is arranged to be set down into the stainless steel pan just described. Its front surface is opened by a sliding curtain, and likewise, its top surface may be opened with a similar curtain. Horizontal front and back motion of the ram and drivehead assembly is accommodated by sliding interlock locking plates so that there will be no leakage of splatter. At the upper portion of the enclosure 131 and behind the drivehead assembly, there is located a ventilator connection elbow 133 adapted to be connected to a suction blower to suck away any steam, fumes, vor gases. The inlet of this elbow is protected by baffles (not shown) to prevent the influx of solid liquid particles.

Turning to the electrolyte supply system, the electrolyte tank 130, which is made of stainless steel, is fitted with an immersion type heater 135 under the control -of a thermostat 137 having an adjustment knob 139. The tank 130 is mounted on wheels 132 as shown, and permanent internal rails and guides 134 are provided fas part of the weldment 1. Temporary guide rails 141 are stored behind access door 143, and these may be mounted with pins so as to constitute forwardly extending rails to permit bringing the tank forwardly on these temporary rails and out onto the door for cleaning or service atten tion. To permit this, the electrical connection for the heater is of the plug in type and the suction line from the tank to the electrolyte pump 145 is made by a standard, quick disconnect coupling 147 and a flexible hose 149. Within the electrolyte tank is a cooling coil 151, which is fed with cold water under control of valve 153. An exit line may be led to the sewer system. The purpose of the cooling coil is to withdraw excessive heat from the electrolyte under those circumstances where heavy working Iand heavy currents would otherwise cause the temperature to rise undesirably.

The electrolyte pump 145 is driven by a motor 155 and is arranged to deliver electrolyte under pressure up to 250 or even 300 pounds per square inch. From the pump 145 the electrolyte passes through a filter 157, which is preferably arranged with quick disconnect fittings to permit easy removal for replacement of filter cartridges. It should be understood that both the tank 130 and the pump 145 and its associated motor and lter are within compartments formed in the weldment 1, and that these c-ompartments are normally closed by hinged access doors, which for purposes of illustration have been cut away in this view.

From the filter 157 the electrolyte passes through a hose line 159, through an electrolyte control panel to a bypass valve 161 seen near the right-hand (or upper) part of the drawing approximately above the midportion of the electrolyte tank. This valve serves Ias a bypass to set the general pressure level and to accommodate variations in the size and working tareas of the electrodes which are being used from time to time. The back pressure created by having closed this bypass valve 161 is indicated on a pressure gauge 163.

A T-connection is taken from line 159 to electrode valve 165, which valves the electrolyte into a header block 167, which is mounted within the electrolyte pan and within the enclosure 131. Optionally, the filter 157 may be connected between the T-connection and valve 165 and this arrangement is preferred. This manifold block may have a number of connections for ease in connecting one -or more electrolyte hoses to feed the electrode as, for example, the hose 27 shown in this illustration. A second pressure gauge 169 `is also connected to the manifold block to indicate the pressure actually Ibeing fed to the electrode. By adjusting the bypass valve 161 to establish the pressure generally desired and by then adjusting electrode valve 165, the pressure being fed to the electrode may be adjusted and maintained. If electrode valve 165 is adjusted so that the pressure in the manifold 167 is somewhat lower than the pressure in the main supply line 159 (as indicated on gauge 163), then as the electrode approaches the work and induces additional restriction to the fiow of electrolyte, .the pressure shown at gauge 169 will rise, and by reference to the reduction in difference between the pressure indicated on the two gauges, the proximity of the electrode to the work may be judged. This is more fully discussed in the copending application Serial No. 772,960, more fully identified above.

Under ordinary circumstances, it is desired that the pressure be held nearly constant although this is not as critical as the feed rate, the voltage, or the temperature of the electrolyte. If, however, there is enough change in the pressure to affect substantially the degree of bubble formation in the work gap or actually within the electrode, then this will mitigate against close accuracy of work. Ordinarily, the operating pressure will not be below two atmospheres, and ordinarily it will not rise above 20 atmospreres or 300 pounds per square inch. A normal working pressure will fall between and 200 pounds per square inch, Ibut it is preferable, once the electrode has become fully imbedded in the work, that the pressure should not vary by more than l0 or 15 percent, and under those condition where maximum` rates of penetration are being used and where the electrolyte in the work gap is just at the verge of -breaking into steam, then even a slight reduction of pressure would be troublesome. However, an increase of pressure of the `order of l0 to 20 percent would not create difficulty. The valving and gauging arrangement which is shown permits, in practice, an easy control of the pressure.

As shown, Ia discharge line 168 extends downwardly from valve 161 as a return to the electrolyte tank 130. In practice, a loop of hose is connected at this point with an elbow at its end which ordinarily discharges electrolyte back into the tank. However, the hose may be withdrawn through an access door (not shown) at the right-hand end of the machine, and the hose may be put into a barrel or other receptacle. Then, by operating the pump 145 and closing electrode valve 165, electrolyte may be withdrawn from the tank and easily discharged without the need for removing the tank. The entire system may, if desired, then be flushed with water, using a hose discharging into the pan beneath the worktable and, thus, owing back through drain openings (not shown) into the tank. It is thus easy to ush the entire system with fresh water and thereby minimize the problem of cleaning.

Normally the heater 135 and its associated thermostat 137 are arranged and adjusted to hold the temperature of the electrolyte sufficiently above ambient temperature so that as energy and, therefore, heat are added to the electrolyte in other ways (for example, by pumping and by the passage of electric current in the work gap between the electrode and the workpiece) the amount of heating provided by heater 135 is automatically reduced by thermostat 137. Accordingly, the heater may be left on overnight to hold a temperature of the order of F. When actual work begins, the pump and the passage of electric current will add energy to the electrolyte and maintain the preset temperature with a reduced demand upon heater 135. Under some conditions, as for example where currents of the order of 1,000 amperes or upward are being passed between the electrode and the work, the heat introduced in this way may be sucient to cause the temperature of the electrolyte to rise in the tank above the desired level of, say 130 1F. Under these conditions, tap water at a much lower temperature (usually in the `range between 50 and 70L7 F.) is introduced by opening valve 153 and causing water to flow in cooling coil 151. By adjusting valve 153, the amount of cooling provided may be so adjusted as to permit the intermittent operation of heater under control of thermostat 137 to maintain the desired temperature. Because the control of temperature is important, a temperature gauge 175 is pro- 7 vided. This is of the type which has a temperature responsive bulb 177 at the end of a shielded tube 179. The bulb is placed in the manifold 167 so that it senses the temperature of the electrolyte very close -to the electrode.

If desired, manual valve 153 may be replaced by a thermostatic valve so that cooling coil 151 is controlled automatically.

The Icontrol of temperature of `the electrolyte is important in maintaining accuracy, and it is preferred that it be held within about or 15 degrees, usually in the range between a low of about 110 and a high of about 175 or 180. As previously suggested, a normal operating temperature will be of the order of 130. If the temperature is increased, this will have the effect under ordinary conditions of causing greater activity of the electrolyte and consequently greater removal, all with the result `that the cavity which is produced is somewhat larger than with a lower temperature.

Thus, it will be seen that to secure accuracy it is desirable to maintain substantially constant the following parameters:

(1) Voltage (2) Feed Rate (3) Temperature of Electrolyte (4) Pressure of Electrolyte.

It will be seen lthat in the apparatus here described, means for controlling all of these have been provided. When all of them are properly controlled it is possible to make holes having straight sides within accuracy of a total error of the order of .002 or less. If, however, the voltage rises and then falls, the hole will be enlarged during that portion of the passage during lwhich the voltage was increased. Similarly, if Ithe feed rate were to decline, the hole would lbe enlarged, or if it were to be increased the hole would be reduced. A rise in temperature causes an enlargement of the hole ordinarily, and a reduction of the temperature reduces the size of the hole. As `to the pressure, as heretofore discussed, itis possible to tolerate a wider range of variation unless one is operating near the critical edge, and one may regard pressure as being important primarily because it affects flow rate which in turn affects the actual temperature of electrolyte in `the Work gap itself, although there are also some primary effec-ts associated with the generation -of bubbles. By holding the pressure at an elevated level, bubbles of gases of electrolysis, principally hydrogen and oxygen, and bubbles of steam are kept small in size, thereby maintaining a high effective density of the electrolyte. If the pressure is reduced, then the bubble size increases, and the effective density is reduced, thereby increasing the effective resistance ofthe electrolyte and, consequently, tending to reduce the electrolyzing current.

Turning now to FIGS. 3 and 4, there is shown apparatus for actuating the dial indicator 23 shown in FIG. 1 and for actuating also a depth limit switch. The dial indicator as such may be purchased as a complete assembly from any of a number of well known suppliers such as Federal, Ames, or Starrett. It is designated in FIGS. 3 and 4 by the reference numeral 23 associated with a bracket which indicates the extent of the purchased assembly. The indicator includes a dial face 23a anda pointer 23b registers with dial indicia indicating a motion of the ram head of .001. One complete revolution of the pointer 23b equals .100. Not shown is a smaller pointer with its own internal dial arranged somewhat like that of the small second hand dial on a watch. This smaller dial has indicia indicating each 0.1, and one complete revolution of this smaller pointer coincides with a motion of 1". Inasmuch 'as the stroke of the apparatus in general is here shown as 8, a rulerlike scale 23C is provided to show grossly the general position of the ram head by reference to a pointer 23a'. The usual knob for adjusting the rotary position .of the dial of the indicator is shown at 23e.

The dial indicator 23 is mounted as by screws 301 and an appropriate bracket to a frame member 303, which in turn is fastened by screws or bolts to the upper housing 5 of the drivehead assembly.

Frame 303 is bored to receive the push rod 19 in a sliding relationship, and it will be recalled that push rod 19 is directly connected to the ram head 11 so that when the ram is moved push rod 19 moves with it. Mounted adjustably to push rod 19 is a carriage 335 having an upwardly extending ear 307 adapted to engage the hardened button at the end of the 'actuator element for dial indicator 23. Here it should be understood that the dial indicator 23 includes a spring which urges the actuating button tothe righlt, as shown in the drawing, so that it will follow any motion of carriage 305 and its upwardly extending bracket 307.

Mounted on carriage 305 is a limit switch 309 having an actuating button 311. A second carriage 313 is slidably mounted on two guide rods 315 and is arranged to be 'moved by rotation of hand knob 49, which is also seen in FIG. 1. Hand knob 49 rotates `a shaft 317 suitably journaled in brackets mounted to frame 303 so as to rotate a sprocket 319, which drives a ball-link chain 321. An idler sprocket 323, suitably journaled, guides the chain at its opposite end. A spring 325 is used to take any slack out of the chain. The ends of the chain are fastened by small lugs 327 to carriage 313, so that rotation of the knob 49 causes carriage 313 to move linearly.

A downward extension 329 of carriage 313 holds a tubular push rod 331 arranged for telescopic sliding action over support and guide rod 133. To the tubular member 331 is affixed a pointer 335 with its tip showing on the scale type indicia 23e of the dial indicator. When knob 49 is turned, therefore, and carriage 313 moves, the pointer 335 also moves so that one can see its position.

Whe-n `the push rod 19 is moved forwardly (to the right in FIGS. 3 and 4) as the ram head advances toward the work, it moves carriage 305 and limit switch 30)v with it, and as will be seen by reference to FIG. 3, the actuating button 311 of the limit switch is arranged so as to be engaged by a frontal surface of carriage 313. The limit switch is wired in such a way as to break the circuits of the holding relays and to deenergize the electric clutches 65 and 67 shown 'in FIG. 2, and to cause electric brake 43 to be set so as to stop rotation of lead screw 31 very quickly. The point at which this occurs in the travel of the ram is determined by the position of the carriage 313, for the farther it is moved to the `left 'as seen in FIGS. 3 and 4, the less distance the limit switch 309 must move before its actuating button engages the frontal surface of carriage 313.

The adjusting knob 49 provides a convenient method of moving the carriage 313, and the entire linkage and slide assembly proves in fact to be sufficient to prevent movement of carriage 313 after it has once been set.

In practice, pointer 335 is used as only a rough guide for the setting of the depth limit control. After the decision has been made as to the depth to which the ram is desired to move, the ram is first moved to that depth with no work in its path, its position being very carefully indicated to less than .001 by the dial indicator and its pointer 23b. Then, the set knob 49 is actuated to bring the carriage 313 toward the depth limit switch 309, and this motion is continued until indicator light 53 (FIG. l) is illuminated, showing that the switch 309 has been actuated. To be sure that the setting is correct, knob 49 is then turned to move the carriage 313 slightly away from the switch and is then turned back -again to bring the carriage very slowly toward the limit switch until the indicator light again flashes to show actuation of the switch. To check the accuracy of the setting, the ram is now slightly retracted by pushing the appropriate control buttons on the console and is then advanced under power. If the setting has been made properly, the ram head will stop at precisely the position determined by the location of carriage 313, and this can be confirmed by the reading on the dial 23a of the dial indicator. Ord-inarily, the advance of the ram will be stopped repetitively within a fraction of a thousandth of an inch of the first stop.

This is used to permit making a series of cavities all to precisely the same depth, and without the need for relying on an operator to watch the dial indicator and to try to stop the apparatus at precisely the same point on each occasion.

A copending application identical in drawings and specifications is being filed concurrently herewith in the name of Mr. Leonard Malkowskii, Serial No. 73,155, now Patent No. 3,130,140, and claims in that application `are drawn to those aspects of the apparatus invented by him.

It will be clear that many variants in the apparatus as described above will be possible without departing from the spirit of the invention. It is therefore desired, by the following claims, to include within the scope of the invention all such variations and modications by which substantially the results of the invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. Apparatus for electrolytically forming a cavity in an electrically conductive and electrochemically erodible workpiece, comprising in combination, means mounting the workpiece, a hollow electrode, means mounting said electrode, means for relatively moving said workpiece mounting means land said electrode mounting means toward each other at a constant rate, an electrolyte supply tank, conduit means connecting said electrolyte tank to said electrode, an electrolyte pump in said conduit means for the delivery of electrolyte under pressure to the gap between the workpiece and said electrode, valve means in `said conduit means for controlling the pressure of the electrolyte, separate heating and cooling means in said electrolyte tank for maintaining the temperature of the electrolyte at a desired level above the .ambient temperature, and means connected to the workpiece and said electrode for passing a low voltage direct current between the workpiece and said electrode in a sense to make the workpiece anodic.

2. Apparatus set forth in claim l, including thermostat means sensing the temperature of the electrolyte closely adjacent the entry to said electrode and connected to control operation of said heating means.

References Cited by the Examiner UNITED STATES PATENTS 2,745,798 5/ 1956 Haueisen 204--224 2,927,191 3/1960 Matulaitis 219-69 2,933,675 4/1960 Hoelzle 204-141 2,939,825 6/1960 Faust 204-143 2,95 8,636 11/ 1960 Hersluiger. 3,002,907 10/1961 Williams 204-143 3,058,895 10/1962 Williams 204--143 3,060,114 10/1962 Sanders 204-143 FOREIGN PATENTS 208,988 6/ 1957 Australia.

595,951 4/1960 Canada.

335,003 9/1930 Great Britain.

W. A. DOUGLAS, Primary Examiner.,

JOHN H. MACK, JOHN R. SPECK, Examiners.

P. SULLIVAN, R. GOOCH, A. B. CURTIS,

Assistant Examiners. 

1. APPARATUS FOR ELECTROLYTICALLY FORMING A CAVITY IN AN ELECTRICALLY CONDUCTIVE AND ELECTROCHEMICALLY ERODIBLE WORKPIECE, COMPRISING IN COMBINATION, MEANS MOUNTING THE WORKPIECE, A HOLLOW ELECTRODE, MEANS MOUNTING SAID ELECTRODE, MEANS FOR RELATIVELY MOVING SAID WORKPIECE MOUNTING MEANS AND SAID ELECTRODE MOUNTING MEANS TOWARD EACH OTHER AT A CONSTANT RATE, AN ELECTROLYTE SUPPLY TANK CONDUIT MEANS CONNECTING SAID ELECTROLYTE TANK TO SAID ELECTRODE, AN ELECTROLYTE PUMP IN SAID CONDUIT MEANS FOR THE DELIVERY OF ELECTROLYTE UNDER PRESSURE TO THE GAP BETWEEN THE WORKPIECE AND SAID ELECTRODE, VALVE MEANS IN SAID CONDUIT MEANS FOR CONTROLLING THE PRESSURE OF THE ELECTROLYTE, SEPARATE HEATING AND COOLING MEANS IN SAID ELECTROLYTE TANK FOR MAINTAINING THE TEMPERATURE OF THE ELECTROLYTE AT A DESIRED LEVEL ABOVE THE AMBIENT TEMPERATURE, AND MEANS CONNECTED TO THE WORKPIECE AND SAID ELECTRODE PASSING A LOW VOLTAGE DIRECT CURRENT BETWEEN THE WORKPIECE AND SAID ELECTRODE IN A SENSE TO MAKE THE WORKPIECE ANODIC. 